Purpose:
Familial exudative vitreoretinopathy (FEVR) is an inherited disorder characterized by the abnormal development of the retinal vasculature. To date, mutations in seven genes have been reported to be responsible for this phenotype (NDP, FZD4, LRP5, TSPAN12, ATOH7, ZNF408 and KIF11). The purpose of this study was to screen these genes in a large international cohort of FEVR patients to determine the mutation frequency of each gene.

Methods:
PCR products were generated from genomic DNA and directly sequenced with primers designed to amplify the coding sequence of the genes and flanking intronic sequence. Whole exome sequencing (Agilent and Illumina) was performed in a subset of cases. Variants were checked for their pathogenic potential using bioinformatics tools including PolyPhen, MutationTaster, SIFT and MutPred. The frequency of variants in control individuals was determined using our in-house database, ExAc and the Exome Variant Server.

Results:
This analysis identified a large number of novel mutations in FEVR patients. Our data show that LRP5, FZD4 and TSPAN12 are the main genes mutated in FEVR and mutations in ATOH7 and ZNF408 are very rare. Our low detection rate of NDP mutations results from the fact that the majority of our cohort had already been pre-screened for this gene. A large number (50%) of our patients had no mutations detected in the known FEVR genes suggesting the presence of mutations not detectable using our screening methodology or that a significant number of new genes remain to be identified.

Conclusions:
We have screened a panel of FEVR patients for mutations in the known FEVR genes. Our data show that the genes encoding known components of the Norrin/β-catenin signaling pathway are primarily responsible for this disorder but that a significant number of patients (50%) have no mutations in these genes.